The present invention relates to the field of mass storage devices. More particularly, this invention relates to an apparatus and method for vibrational dampening of the actuator assembly and the base of a disc drive.
One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are an information storage disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. The transducer is also said to be moved to a target track. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track.
The methods for positioning the transducers can generally be grouped into two categories. Disc drives with linear actuators move the transducer linearly generally along a radial line to position the transducers over the various tracks on the information storage disc. Disc drives also have rotary actuators which are mounted to the base of the disc drive for arcuate movement of the transducers across the tracks of the information storage disc. Rotary actuators position transducers by rotationally moving them to a specified location on an information recording disc.
The actuator is rotatably attached to a shaft via a bearing cartridge which generally includes one or more sets of ball bearings. The shaft is attached to the base and may be attached to the top cover of the disc drive. A yoke is attached to the actuator. The voice coil is attached to the yoke at one end of the rotary actuator. The voice coil is part of a voice coil motor which is used to rotate the actuator and the attached transducer or transducers. A permanent magnet is attached to the base and cover of the disc drive. The voice coil motor which drives the rotary actuator comprises the voice coil and the permanent magnet. The voice coil is attached to the rotary actuator and the permanent magnet is fixed on the base. A yoke is generally used to attach the permanent magnet to the base and to direct the flux of the permanent magnet. Since the voice coil sandwiched between the magnet and yoke assembly is subjected to magnetic fields, electricity can be applied to the voice coil to drive it so as to position the transducers at a target track.
When, however, electricity is applied to the voice coil to generate a drive force to relocate the transducer attached to the rotary actuator assembly, the permanent magnet and yoke are subjected to the resulting reaction force. The permanent magnet and yoke are attached to the base of the disc drive. The reaction force acts through the permanent magnet and yoke to excite the base. Simply put, the base is vibrated when the voice coil is used to move the actuator and transducers during a seek operation. As a result, during positioning, there occurs a relative displacement between the transducer supported by the actuator assembly and the track on the disc. This causes the transducer to move off-track. In addition, access times to data can increase. At the end of a seek, the transducer must settle to a position over a track. If the disc and attached base are vibrating, the track below the transducer may be moving thereby preventing the transducer from xe2x80x9csettlingxe2x80x9d. As a result, the time required for positioning increases, thereby affecting positioning performance such as access time. Tracks are becoming narrower and narrower as tracks are being placed closer and closer together. The problems of settle time are also exacerbated by the decreased widths.
After a seek, the disc drive may be commanded to write data to a track. If the transducer is vibrating or moving beyond a selected limit, then a write fault is declared to prevent overwriting or corruption of an adjacent track. The selected limit may be called a write fault threshold or can also be referred to as an on cylinder limit. As tracks get narrower and narrower, it becomes increasingly more important to reduce the relative movement between the track on the disc and the transducer to lessen the chance of read errors or write faults. In most cases, when a write fault occurs, the actuator remains on track until the transducer is repositioned over the proper sector. The actuator remains on track for at least one revolution. When the transducer is again positioned over the proper sector, a write can occur provided that the actuator is within the write fault threshold. If not within the write fault threshold at the target time, the procedure of waiting on track and retrying a write is repeated either for a selected number of revolutions until the actuator is within the write fault threshold at the target time. Then a write can occur. Low levels of write fault errors are tolerable or acceptable. However, when too many write faults occur over a given amount of time, the performance of the disc drive degrades. In summary, when an excessive number of write fault errors are encountered over a given amount of time, the average seek time degrades significantly.
In the past, several approaches have been used to try and minimize the movement of the base as it reacts to the driving force produced by the voice coil motor. The approaches all use dynamic weights. In other words, the weights move significantly with respect to the disc drive base. Such approaches can also have problems. There is always a distinct possibility that the movement may cease over time. In other words, the rings or weights or comer weight may become stuck. The result is that all of the sudden a disc drive may begin to produce large numbers of read and write errors. The disc drive, simply put, would be less reliable. There is also a chance that there may be particles generated from two parts rubbing whenever one part is moving with respect to another. Such particles can cause disc crashes when they are within the disc enclosure.
Quick and precise positioning requires the reduction of the vibration of the magnetic disc apparatus caused by the driving reaction force to the voice coil motor. What is needed is a disc drive which has is less susceptible to the reaction forces. This will improve settling characteristics after a seek from a first track on the disc to a target track on the disc and will improve track following operations of the disc drive. In other words, there is a need for a disc drive that has less relative motion between the actuator assembly and the base while under any type of servo control that requires corrections to be implemented with the voice coil motor. There is also a need for a static solution so that the resulting disc drive is more reliable over the life of the drive. Also needed is a device that can be assembled using current assembly techniques.
The inventive disc drive includes a bead disc enclosure, and a device for increasing the inertia of the head disc enclosure attached to the head disc enclosure. The disc drive includes a base and a disc rotatably attached to the base. The disc drive also includes an actuator assembly rotatably attached to said base and a device, such as a voice coil motor, for moving the actuator assembly. A cover is attached to the base. The combination of the cover and the base form a disc enclosure for enclosing the disc, the actuator assembly and the voice coil motor. An inertia ring is attached to the disc enclosure for increasing the moment of inertia of the base and cover. The inertia ring may be attached to the cover or to the base. The inertia ring is generally formed of a high density material. In some embodiments, the inertia ring may also be formed integral with the base or the cover. The inertia ring may also be formed and positioned such that most of the material of the inertia ring is positioned near the periphery of the base and attached cover. The inertia ring may be formed to attach to the cover so that the ring fills a void between the disc and the attached cover.
Advantageously, the inertia ring reduces the vibration of the magnetic disc apparatus from the driving reaction force to the voice coil rotor. In other words, the added mass and position of the mass near the periphery of the disc drive makes it less susceptible to the reaction forces. Settling characteristics after a seek from a first track on the disc to a target track on the disc is improved. Track following operations of the disc drive are also improved. The disc drive has less relative motion between the actuator assembly and the base while under ally type of servo control which implements course corrections using a driver such as a voice coil motor. The solution is also static. In other words, the inertia ring does not move substantially with respect to the remaining portion of the disc drive. As a result, the disc drive is more reliable over its life. The addition of the inertia ring to the disc drive during manufacture can easily be accommodated using current assembly techniques.